Air heater



Nov. 12, 1929. c. wf E. CLARKE AIR HEATER Filed March 11, 1924 7 Sheets-Sheet 'l Nov. 12, 1929. c. w. E. CLARKE 1,734,962

AIR HEATER Filed March 11, 1924 7 sheets-sheet 2 Nov. 12, 1929. c. w. E. CLARKE AIR HEATER Filed March l1. 1924 7 Sheets-Sheet 3 ImJHoNHIblHnDWHHHIIIIhIIHHnUH ullhnHld HNHHHIIHIIIUIHMHL INVENTOR 6, 21./6. 6 M

ATTORNEYS N.V 12, 1929 v c. w.-E. CLARKE 1,734,962

AIR HEATER Filed Ma1jh 1.1. 1924 7 Sheets-Sheet 4 kIZB lgln /Z =v= s N m v y a? /fo 76 24 77 y) lz- 46 Eknmunnmlu 45 ZZ HIIIIIIIIII- 34 Vf 48 54 4@ /os 50 //o m l INVENTOR Mci f/m,

ATTORNEY;

Now'g. l2, 19.29.A c. w. E. CLARKE AIR HEATER 7 Smets-Sheet 5 .Filed March 11, 1924 INyENTR @h/6,6%,"

A BY f4 QW W ATTORNEYS Nov. l2, 1929.

c. w. E. CLARKE l AIR HEATER Filed March 11. 1924 7 Sheets-Sheet 6 I xNvENToRy 21./ 612a/1@ ATTORNEYS Nov. l2, 1929. c, E CLARKE 1,734,962

AIR HEATER Filed March 11, 1924 'r sheets-sheet 'I INVENTOR www ATTORNEYS Patented Nov. 12, 1929 UNITED STATES PATENT OFFICE CHABLIS WARRINGTON EABLE CLARKE, OF NEW YORK, N. Y., ASSIGNOB T LUCIIALE l V. CLARKE, 0F PHILADELPHIA, PENNSYLVANIA .AIB HEATER Application led March 11, 1924. Serial No. 698,405.

My invention relates to apparatus for heating air or other gases, and nas special reference to that class of heating apparatus which is employed for heating air or gases by the s waste heat from furnaces.

An object of the invention is to provide an apparatus of this character which is simple, strong and rigid in construction and highly ciicient in operation.

Another object of the invention is to provide a novel and improved heating element for an apparatus of this character.

Another object of the invention is to provide an apparatus of this character in which the heating elements are mounted in a novel and improved manner.

With these and other objects in view the features of the invention consist in certain constructions, arrangements and combinations of parts hereinafter described and claimed, the advantages of which will be obvious to those skilled in the art.

i ne several features of the invention will be clearly understood from the following description and accompanying drawings, in which,

Figure 1 is a front elevation, part-ly in section, of an air heating apparatus embodying the features of the invention in their preferred form, the air heater being shown insorted in the uptake iiue of a furnace;

Fig. 2 is a sectional plan view, partly broken away, taken substantially on the line 2--2 of Fie'. 1'

LFig.7 3 is a sectional plan View, on an enlarged scale, taken on the line 3-3 of F ig. 1;

Fig. et is a detail sectional plan view taken on the line -l-4-. of Fig. 1:

Fig. 5 is a side elevation, with certain parts removed and partly broken away, of the apparatus illustrated in Fig. l;

Fig. 6 is a detail sectional view on an enlarged scale taken on the line 6-6 of F ig.v 5;

Fig. 7 is a sectional view, on an enlarged scale and partly broken away, taken substantially on the line 7-7, of Fig. 2;

Fig. 8 is a det-ail side elevation of a heating element forming a component part of the heating apparatus;

Fig. 9 is a sectional view, on an enlarged scale, taken on the line 9-9 of Fig. 8;

Figs. 10 and 11 are detail sectional views taken on the lines 10-10 and 11--11, respectively, of Fig. 7

Figs. 12 and 13 are detail views in perspective tof component parts of the heating elemen 5 Fig. 14 is a view similar to Fig. 8 but showing a modified construction of heating element;

Fig. 15 is a sectional view taken on the line 15-15 of Fig. 14 and showing a plurality of the heating elements assembled;

Figs. 16 and 17 are detail sectional views, on an enlarged scale, taken on the lines 16-16 and 17-17, respectively, of Fig. 111;

Figs. 18 and 19 are views in perspective of component parts of the heating elements illustrated in Fig. 14;

Fig. 2() is a view in perspective of one of the plates of the air heating element illustrated in Fig. 8; and

Fig. 21 is a similar view of one of the plates of the air heating element illustrated in Fig. 14.

The air heating apparatus illustrated in the drawings is provided with a casing which is arranged vertically and has its lower end connected with a header 2 which may lead from the iue gas outlet of a boiler furnace, and has its upner end connected with a header 4 which may lead to the furnace chimney. This casing is provided with front and rear Walls 6 and 8, respectively, and with side walls l0. The casing is divided by partitions 12 into two air heating sections 14 and 16 having a gas by-pass 18 between them which is adapted to be opened and closed by means of a damper 2T). Each of the side walls 10 of the casing is provided with an air inlet opening 22 which may be open to the atmosphere or may he connected by a conduit 24 with a source of air supply, and is further provided with an air outlet opening 26 which may be suitably connected by a conduit 28 with the wind box of the furnace. This arrangement of air heat ing elements with a by-pass between them is the same as in the apparatus described and claimed in my pending'application, Serial No. 620,162, tiled February 20, 1923.

Each air heating section 14 and 16 of the casing contains a plurality of air heating elements 30 arranged vertically side by side and spaced apart and extending between the side wall 10 of the heating section and the partition or wall l2. Each air heating element comprises two plates 32 and 33 (Figs. 8 and 9) that are arranged side by side and spaced apart. In the illustrated construction the plates are elongated and substantially rectangular and one of the longitudinal edges of each of them is provided with two projecting marginal portions or flanges 34, the upper end of the upper flange 34 being spaced a slight distance from the upper end of the plate, and the lower end of the lower llange 34 being spaced a slight distance from the lower end of the plate. The marginal portions 36 of the plates between the inner ends of the flanges 34, the marginal portions 38 at the ends ot the plates, and the marginal portions 40 at the other longitudinal edge of the plates are bent over so as to bring their edges together when the plates are assembled, and when assembled their edges are welded together so as to form air tight joints that are substantially V-shape in cross section. Each projecting liange 34 is bent outwardly so as to form an inclined portion 42 and is then bent to form a portion 44 in a plane parallel to that of the body of the plate. The openings at the lower and upper outer corners of each heating element are closed by castings 46 of suitable shape to enable them to be inserted between the plates, (Figs. 7, 10 and 12). Each corner-piece or casting 46 is provided with langes 48 on the longitudinal edges of its inner side that engage the associated end portions ot the plate flanges 34, and are further provided with a ll-shaped lug 50 on the inner end portion ot its outer side that extends int-o the V-shaped space between the outer ends of the associated end marginal portions 38 of the plates. rlhe space between the inner ends ot the plate flanges 34 of each pair is closed by a casting 52 having inwardly projecting flanges 54 on its longitudinal edges engaging the inner sides of the plate flanges 34, and having its inner end portion extending over the adjacents ends of the central marginal portions 36 of the plates. rlhe castings 46 and 52 are welded to the plates so as to form tight joints. The upper and lower pairs of flanges 34 of the plates and their associated castings 46 and 52 detinethe air inlet and outlet openings, respectively, ot the heating element.

In the illustrated construction the interior ot each heating element 30 is divided into a plurality or" passages having their inlet and outlet ends arranged adjacent to the inlet and outlet openings, respectively, in the element. IThese passages are :formed by angle avsaeea irons 66 having intermediate vertical portions 68 that are equally spaced, and having their ends turned toward the inlet and outlet openings ot the heating clement so as to form horizontal portions 70. Angle irons 72 are also provided at the inner corners of the interior of each heating element so as to form portions of the outer wall of the outermost passage, these angle irons being curved concentrieally with the curved portions of the inner wall of the passage. The ends of the angle irons 66 are so spaced as to cause the shorter air passages to be restricted or throttled at their ends, the passages being thus throttled progressively in decreasing degrees from the shortest to the longest passage. The extent of such throttling of the air passages at their ends is in proper proportion with relation to the Variation in the lengths of the passages as to cause the air passing through the passages to be distributed evenly over the entire surfaces of the plates, and to prevent any tendency to short circuit through thil shorter passages. The angle irons 66 and 72 in addition to forming the passages through the element, constitute stillening and spacing members for the elongated plates. As shown, the angle irons are held in position by having one of their sides welded to the plate 33 so that when the plates are assembled the edge of the other side of the angle irons will tightly engage the plate 32.

ll/hen the heating elements are assembled in the heating sections of the casing they are held spaced apart by means ot angle irons 74 which extend longitudinally of each plate 32, a side of each angle iron being welded to the plate opposite to the vertical portions 68 ot' the angle irons 66. rlhese vertical angle irons 74 in addition to constituting spacing members for the heating elements also constitute still'ening members for the plates. The angle irons 74 also provide for proper distribution ot the gas and the amount of work through the heater, acting as guides tor the same.

The heating elements are inserted in the heating sections of the casing through the outer sides of the sections and are so positioned in each heating section as to cause the casting 46 at the lower end of the outlet opening ot each element to rest upon the hori- Zontal side ot an angle iron 7 6 extending tore and aft of the casing, each angle iron 76 being secured by bolts 8O upon channel irons or beams 78, and the lower outer corners ot' the heating elements abutting the inner sides of the beam 78. The heating elements of each section are held in position on the channel iron 76 by the engagement of the upper end portion of their inner longitudinal margins between blocks 81 which are secured by bolts 82 to the partition 12 (Figs. 1 and 4).

ln inserting the heating elements in the section 16 o'i the casing they are positioned or llO ' walls, the bars 86 restin 'S8 Welded to the rear wal laid against the front wall 6 of the casing, with the side of the heating element upon which the angle irons 74 are secured directed to the rear, the 'Wall 6 being provided with vertically arranged angle irons 84 welded thereto so as to space the first heating element inserted from the wall. When all the heating elements have been thus inserted la plurality of bars 86 are forced horizontally between the last heating element andthe rear wall 8 of the casing so as to hold the elements iirmly together between the :front and rear upon angle irons The heating elements are inserted in the section 14 of the casing in a similar manner except that they are iirst laid against the rear wall 8 of the casing, the rear wall being provided with spacing angle irons 90 corresponding to the angle irons -84, and the heating elements being firmly held together by means of bars 92 resting upon angle irons 94 corresponding to the bars 86 and angleirons 88. By placing the heating elements into the sections in this man-A ner it will be apparent that the heating elements for both sections may be of the same construction.

Vhen the heating elements are mounted in each section, as above described, the outer portions 44 of the flanges 34 of adjacent heating elements are positioned in engagement, and' these engagin portions are welded together to form air tig t joints. The spaces between the outer flanges 34 of the end heating elements and the front and rear walls of the casing may be closed by suitably arranged strips 96 welded to the flanges and to said walls.

The angle irons 76 upon which the lower outer corners of the heating elements of the two heating sections are mounted constitute the bottom walls of the outlet openings 26 in the heating sections, and angle irons of the same construction constitute the top wall of each outlet opening and the top and bottom walls of each inlet opening of the heating sections, the angle irons extending over the outer sides of the castings 46 and 52. The angle irons 76 forming the top wall of the outlet openingr 26 and the bottom wall of the inlet opening 22 are supported by means of angle irons 100 having their horizontal sides extending over the outer sides of the angle irons 76 and having their vertical sides projecting towards each other and extending across the central marginal portions 36 of the heating elements. A similar angle iron 102 has its' horizontal side extending over the inner portion of the angle iron 7 6 that forms the top wall of each air inlet opening 22. The castings 52, the adjacent angle irons 76 and the angle irons 100 are secured together by means of bolts 104 (Fig. 7) that extend through apertures in the castings 52 of the air heating elements. The castings 46 at the upper ends of the inlet openings of the heating element or each heating section, the adjacent angle iron 76 and the angle iron 102 are secured together by means of bolts 106 that extend through apertures in said castings 46. A metal strip 108 and a strip 110 of asbestos or other suitable material arranged side by side areinterposed between each of the angle irons 7 6 and the adjacent end walls of the air inlet and outlet openings of the air heating elements that are formed by the castings 46 and 52 so as to provide tight joints. The side walls of the air inlet and outlet openings 22 and 26 of each heating section are formed by channel irons 112 extending be tween the angle irons 76 of each opening, the channel irons being riveted to angle irons 114 secured to the outer margins of the front and rear walls of the casing. The space between the angle irons 100 of each heating Section is closed by a plate 120 whichI is secured by bolts 122 to the vertical sides of said angle irons, the plates being made in sections that are connected by abutting angle irons 123 so as to enable the plate to be applied and removed in sections, handles 124 being secured to each section.

The vertical sides of the angle irons 114 are secured by bolts 126 to the vertical sides of angle irons 128 having their ends secured to angle irons 130 that are secured on the outer margins of the upper ends of the front and rear walls of the casing. The horizontal sides of the angle irons 128 and 130 form a flange to which the flange of the header 4 may be connected. Angle irons 132 are secured to the outer margins of the lower ends of the front and rear walls of the casing and extend between the supporting channel irons or beams 78, the ends of the angle irons being secured to the beams by means of angle irons or corner pices 133. The horizontal sides of the angle irons 132 and the lower flanges or sides of the beams 78 form a flange to which the header 2 may be connected.

The upper end portion of the partitions 12 which support the upper inner end corner portions of the heating elements, as hereinbefore described, are supported or reinforced by a frame 134 comprising channel irons or beams 136 th at are secured to the partitions by the bolts 82 that secure the spacing blocks 81 to the partitions; and suitably arranged struts 138 extend between the channel irons or beams 13650 as to form a rigid construction. Horizontal channel irons or beams'l40 are secured to the outer sides of the front and rear walls of the casing opposite the ends ofthe beams 136 and the ends of the beams 140 are supported by downwardly and outwardly inclined struts 128 secured to and extending to the lower outer corners of said side walls.

From the foregoing it will be apparent that an air heater of the plate heater type is provided in which there is no danger-of leakage between the air and gas passes as all the joints between these two sets of passes are welded so as to tightly seal them; and the provision of the V-shaped joint between the edges of the plates of each heating element permits the free entrance of gases to gas spaces of heater elements without causing undue eddies or objectionable draft loss. It will also be apparent that as the air in passing through each element is uniformly distributed, as hereinbefore described, throughout the entire area of the interior of the element, the entire area of each plate is uniformly utilized in heating the air. By arranging the heating elements in the heating sections of the casing at opposite sides ot' the gas by-pass 18; supporting the elements in such a manner that their lower outer corners rest upon the large channel irons or beams 87 and are held in position on the beams by the engagement of their diagonally opposite corner portions with the spacing blocks 81 on the inner walls or partitions 12 which are reinforced by the supporting frame; and by firmly binding the heating elements together between the front and rear walls of the casing, it will be apparent that the large and relatively thin plates of the heating elements are firmly and rigidly supported without placing any undue strain upon them that would have a tendency to weaken or open up their welded joints. The channel irons or beams 78 in addition to bearing the weight of the heating elements also support substantially the entire wei ht of the casing of the heater, the lower en s of the supporting struts 128 extending to the lower outer end corners of the front and rear walls of the casing.

The modified construction of heating element illustrated in Figs. 14 to 19, inclusive, comprises two plates 141 and 142 which are arranged side by side and spaced apart, the plate 141 having angle irons secured onits inner side corresponding to the angle irons of the heating element illustrated in Fig. 8, and the plate 142 having vertically arranged angle irons 146 secured on ,its outer side corresponding to the irons 74 ot the heating element illustrated in said figure. In this construction, the plate 141 is ilat throughout its area and is substantially rectangular. One of the longitudinal edges of the plate 141 is provided with two projecting marginal portions or flanges 148, the upper end ot the upper flange 148 being spaced a slight distance from the upper end of the plate and the lower end of the lower flange being spaced a slight distance from the lower end of the plate. The plate 142 corresponds substantially in contour to the plate 140 but has one of its edges provided with two marginal portions or flanges 150 that are bent outwardly as shown to privide an outwardly inclined portion 152 and a portion 154 in a plane parallel with the plane of the body of the plate. The margin of the portion of the plate 142 between the flanges 150, the end margins of the plates, and the margin of the other longitudinal edge of the plate, are bent inwardly at an angle to bring their edges against the corresponding edge portions ofthe plate 141, the edges of the two plates being welded together so as to form air and gas tight joints.

T he openings at the upper and lower outer corners of each heating element are closed by castings 156 and 157, respectively, of suitable shape to enable them to be inserted between the plates. Each corner-piece or casting is provided with ilanges 158 on the longitudinal edges of its inner side that engage the associated end portions of the plate l'langes 148 and 150, and are further provided with a V-shaped lug 160 on the inner end portion of its outer side that extends into the space between the outer ends of the associated end marginal portions of the plates. The space between the inner ends of the plate flanges 148 and 15() of each pair is closed by a casting 162 having inwardly projecting flanges 164 on its longitudinal edges engaging the inner sides of the plate flanges, and having its inner end portion extending over the adjacent ends ofthe central marginal portions of the plates. When the heating elements are assembled as illustrated in Fig. 15 they are held spaced apart by the angle irons 146 and the horizontal portions 154 of the plates 142 lie against the flanges 148 of the plates 140, which contacting portions of the flanges of the two plates are welded together so as to form gas tight joints. It will be apparent that this construction of heating element is desirable as only the margins of one of the plates of the heating element are bent over, the other plate'of the heating element being left flat throughout its area, thus providing a construction that is simple and cheap as well as strong and rigid.

In constructing each plate of the air heating element illustrated in Fig. 8, a substantially flat sheet is provided which is cut to form a substantially rectangular body portion, Fig. 20, having one of its longitudinal edges provided with two projectingl marginal portions adjacent the ends thereof forming the flanges 44, the upper projecting portion or flange having its upper end spaced a slight distance from the upper edge of the body of the plate, the lower projecting portion having its lower end spaced a slight distance from the lower edge of the body portion, and the inner ends of said projecting portions or flanges being spaced a distance apart. The inner longitudinal portion ot each of said portions or flanges 34 are bent to form the inclined portion 42, and the outer portion 44 which is arranged parallel with the body of the plate. The ends of the central marginal portion 36 between the inner ends of said anges 44 is slitted at 170, and

this central marginal portion is bent in the opposite direction to the inclined portion 42 of the flanges. The opposite corners of the plate at the ends of the other longitudinal edge are provided with diagonal slits 172, and the marginal portion of this longitudinal edge and the marginal portions of the ends of the body of the plate are bent in the same direction as said central marginal portion 36. The slits 172 are of suitable shape so that when the marginal portions of the latter longitudinal edge and the ends of the plate are bent the edges of the adjacent ends thereof are brought together and these edges are then welded, which completes the formation of the plate. It may be noted that both of the plates of the air heating element illustrated in Fig. 8 are constructed in the manner above described and are interchangeable. The two plates are assembled to form the heating element after the angle irons 68 have been applied to one of them, as hereinbefore described, by bringing the plates t0- gether with the edges of the inwardly bent marginal portions of the plates positioned in engagement, and then welding these edges together.

It may be noted that the plate 14,2 illustrated in Fig. 21 is constructed'in the same manner as the plate 32 illustrated in Fig. 20, except that the bent marginal portions, and also the flanges 154 are wider than the corresponding parts of the plate 32.

As will be evident to those skilled in the art, my invention permits of various modications without departing from the spirit thereof or the scope of the appended claims.

What I claim is:

1. A heating element for an air heater comprising two plates arranged side by side and spaced apart, and having inlet and outlet openings for enabling air to be passed through the space between said plates, said space being divided into a plurality of air passages having their ends in communication with said inlet and outlet openings, said air passages being of diii'erent lengths, and the shorter air passages being suitably throttled to effect a uniform distribution of the air through said space.

2. A heating element for an air heater, comprising two plates arranged side by side and spaced apart, with the space between their edges closed, one of the longitudinal edges of the element thus formed having openings therein arranged adjacent its ends, respectively, and a plurality of'partitions arranged in the space between said plates and having their ends directed toward said openings so as to provide a plurality of air passages extending through said element, said partitions being suitably spaced different distances apart to effect a substantially uniform distribution of air through said space between the plates.

3. A heating element for an air heater, comprising two plates arranged side by side and spaced apart, at least one of the plates having marginal portions of one end bent toward the edge of the corresponding end of the other plate, the edges of said ends' of the plates being welded to ether, one of the longitudinal edges of the plates having projecting marginal portions having one end of each of them spaced a distance from said welded edges, and a stiffening member extending into and closing the space between said end of said longitudinal marginal portions and having a projecting lug extending into and closing the space at the adjacent end (if said welded edge portions of the plates.

4. An air heater having, in combination, a plurality of plates arranged vertically side by side and spaced apart so as to provide alternate air and gas passes, the lower edge of at least one of the plates being bent toward the lower edge of the other plate with the two edges welded together, one of the longitudinal edges of each element thus formed having inlet and outlet openings adjacent its ends, respectively, so as to enable air to be passed through the space between the plates, a casing enclosing said plates having its lower end adapted to be. connected with the flue gas outlet of a furnace and having its upper end adapted to be connected with the chimney flue, one of the walls of said casing having inlet and outlet openings connecting with all of said inlet and outlet openings, respectivel of said elements.

5. A heating e ement for an air heater comprising two plates arranged side by side and spaced apart, one of the plates having marginal portions bent toward the other plate with their edges welded to the edge of the other plate, other marginal portions of one edge of one of the plates being bent outwardly so as to form inlet and outlet openings adjacent the ends, respectively, of the element thus formed, and sti'l'ening members closing the spaces at the ends of said outwardly bent portions and welded to the plates.

6. A heating element for an air heater comprisin two plates arranged side by side and space apart, one of the plates having marginal portions bent toward the other plate with their edges welded to the edge of the other plate, other marginal portions of the plates at one edge of the element thus formed projecting a distance and having their outer ends spaced from the adjacent ends of the plates, respectively, so as to form a corner at each end of said edge, and stifeningv members closing the spaces at said corners and welded to said plates.

7. An air heater having, in combination, a casing, a plurality of heating elements, each comprising two plates arranged side by side and spaced apart with the space between their longitudinal edges closed, one of the eoA longitudinal edges of each of said elements having inlet and outlet openings adjacent its ends, respectively, said inlet and outlet openings in all of said elements being in communication with inlet and outlet openings, respectively, in said casing, and spacing members arranged between the adjacent elements and secured to but one of said elements so as to enable said elements to be separately pesitioned within the casing.

8. An air heater having, in combination, a casing having open ends adapted to be connected with the flue gas outlet and chimney iue of a furnace, respectively, a plurality of air heating elements arranged side by side and spaced apart within the casing so as to provide gas passes between them and having inlet and outlet openings leading out through a side wall of the casing, and an opening in a side wall of the casing closed by a removable cover so as to enable access to be had to the. spaces between said elements.

9. An air heater having, in combination, a casing, a plurality of air heating elements arranged within said casing and spaced apart, each of said elements comprising two plates arranged side by side and spaced apart, and having the space between their edges closed, the longitudinal edge of one of the plates of adjacent elements having portions bent toward the other plate with their edges welded to the edge of the other plate, said portions of each element forming inlet and outlet openings in communication with inlet and outlet openings, respectively, in the casing.

10. An air heater having, in combination, a series of elements vertically arranged side by side and spaced apart, each element being made of two plates arranged side by side and spaced apart and having suitably arranged openings for enabling air to pass therethrough, and supporting members engaging diagonally opposite corners of said elements for supporting them, the upper supporting members engaging merely the longitudinal edges of the elements so as to permit both longitudinal and lateral expansion of the elements.

11. An air heater having` in combination, a series of elements arranged vertically side by side and spaced apart, each element being made up of two plates arranged side by side and spaced apart having suitably arranged openings to enable air to pass therethrough, a support upon which one of the lower corners of each element rests, and means engaging each element adjacent a diagonally opposed corner thereof for holding said elements in vertical position on said support, the upper supporting members engaging merely the longitudinal edges of the elements so as to permit both longitudinal and lateral expansion of the elements.

12. An air heater having, in combination, two substantially rectangular plates arranged side by side and spaced a art, one of the plates being substantially at and the other plate having marginal portions bent toward said flat plate with their edges welded to the corresponding parts of the edge of said flat plate, the element thus formed having openings located in one of the longitudinal edges thereof and adjacent its ends, respectively, each of said openings being formed by projecting marginal portions on the two plates and stitfening members 'closing the space between the ends of said marginal portions.

13. An air heater having, in combination, a plurality of plates arranged side by side and spaced apart so as to provide alternate air and gas passes, the plates defining each air pass having the space between corresponding edges thereof closed by the marginal portion of at least one of them being bent toward the other with the two edges welded together, one of the other edges of each element thus formed having inlet and outlet openings adjacent its ends, respectively, so as to enable air to be passed through the space between the plates, a casing enclosing said plates having the end thereof adjacent said corresponding edges of said plates adapted to be connected with the line gas outlet of a furnace and having its other end adapted to be connected with the chimney flue, one of the walls of said casing having inlet and outlet openings connected with all of said inlet and outlet openings, respectively, of said elements.

14. An air heater having, in combination, a plurality of plates arranged side by side and spaced apart to provide alternate air and gas passes, a support upon which one of the lower corners of the plates rests, and means engaging the diagonally opposite corner of the plates to provide a lateral support for holding the plates in position on said support.

15. An air heater having, in combination, a plurality of substantially rectangular plates arranged vertically side by side and spaced apart to provide alternate air and gas passes, a support upon which one end portion of the lower edges of the plates rest, and means engaging the upper end portions of the opposite longitudinal edges of the plates for holding the plates in position on said support.

16. A heating element for an air heater comprising two plates arranged side by side and spaced apart, at least one of the plates having marginal portions bent toward the other plate with their edges welded to edge portions of the other plate, other marginal portions of said plates being spaced apart so as to provide inlet and outlet openings in the element thus formed, and stiftening members closing the spaces at the ends of said spaced marginal portions and welded to the plates.

CHARLES WARRINGTON EARLE CLARKE. 

